The following definitions will assist in understanding various abbreviations used in this document:    3GPP 3rd Generation Partnership Project    ACK Acknowledgement    BER Bit Error Rate    BW Bandwidth    CDM Code Division Multiplexing    CRS Common (Cell-specific) Reference Signal    CSI-RS Channel State Information Reference Signal    CSS Common Search Space    CoMP Collaborative Multi-Point    DCI Downlink Control Information    DL Downlink    DM-RS Demodulation Reference Signal (UE specific)    eCCE enhanced Control Channel Element    eNB enhanced Node B (LTE base station)    EPBCH Enhanced Physical Broadcast Channel    EPDCCH Enhanced Physical Downlink Control Channel    EPHICH Enhanced Physical Hybrid ARQ Indicator Channel    EPREG EPHICH Resource Element Group    eREG enhanced Resource Element Group    FFS For Further Studies    HARQ Hybrid Automatic Repeat Request    HetNet Heterogeneous Network    IMR Interference Measurement Resource    LTE Long Term Evolution    MIB Master Information Block    NACK Negative ACK    NCT New Carrier Type    OFDM Orthogonal Frequency Division Multiplexing    OFMDA OFDM Access    PBCH Physical Broadcast Channel    PCell Primary Cell    PHICH Physical Hybrid ARQ Indicator Channel    PRB Physical Resource Block    PUSCH Physical Uplink Shared Channel    RRC Radio Resource Control    RE Resource Element    REG Resource Element Group    RS Reference Signal    SF Spreading Factor    TDD Time Division Duplexing    UE User Equipment (e.g. Mobile Terminal)    USS User specific Search Space    WG Working Group
As the number of wireless cellular data communication devices continues to increase and as their data capabilities continue to be more and more heavily used, the demands on available infrastructure and frequencies continue to increase. The addition of infrastructure to meet demand is costly, and is becoming more and more difficult as unoccupied space suitable for placement of larger base stations diminishes. In addition, as saturation of available wireless communication frequencies approaches, addition of conventional infrastructure approaches a point of ineffectiveness. Network operators are therefore under constant pressure to improve the efficiency of their use of resources, particularly frequency resources. One important aspect of efficient use of resources is the efficient use of control signaling, and mechanisms such as decreasing the control signaling required and increasing the detectability of control signals can substantially improve communication efficiency.